Process for the purification of tobacco smoke



United States Patent O 3,288,150 PROCESS FOR THE PURIFICATION OF TOBACCO SMOKE Oliver W. Burke, Jr., 506 Intracoastal Drive, Fort Lauderdale, Fla., and Eldon E. Stahly, Pompano Beach, Fla; said Stahly assignor to said Burke No Drawing. Original application Aug. 13, 1963, Ser. No. 301,879. Divided and this application Aug. 7, 1964, Ser. No. 398,463

1 Claim. (Cl. 131-261) The present application is a division of application Serial No. 301,879 filed August 13, 1963 and has been filed pursuant to a requirement for restriction made in said application Serial No. 301,879, under 35 U.S.C. 121.

This invention relates to the improvement of tobacco smoke, filters, and cigarettes for the reduction of metal content, e.g., metal carbonyls, in the smoke. Strictly speaking, a metal carbonyl is a compound of metal and carbon monoxide, but in a broader sense the term metal carbonyl also includes the analogous metal nitrosyl carbonyls and the metal hydrocarbonyls, which are similar compounds in which one of the carbonyl groups has been replaced by a nitrosyl or 'a hydrocarbonyl group, and except where the context indicates to the contrary, the term is employed in said broader sense herein. Metals may also be present in the smoke in other forms, and the term metal content of the smoke has reference to the metal present therein Whether in the form of gaseous metal carbonyl compounds or otherwise.

Objects of the invention, severally and interdependently, are to provide an improved cigarette having a substantially reduced content of metal in its smoke output as compared to conventional plain or filter-tipped cigarettes; to provide a process for the purification of tobacco smoke by removing metals therefrom by converting the same to non-volatile materials; to provide an improved cigarette smoke from which selected metals are substantially reduced or eliminated; to provide an improved method and cigarette, or cigarette filter, in which metals present in tobacco smoke in small amounts are converted to forms, e.g., non-volatile materials, in a manner which effectively prevents their leaving a cigarette in the smoke; and to provide an improved method and cigarette in which a ligand material is reacted with metals in the tobacco smoke and converts them into non-volatile compounds.

Other objects and advantages of the invention, and of preferred embodiments thereof, will be apparent from the following description and from the illustrative examples appended thereto.

The invention resides in the new and useful methods and products herein disclosed, and is more particularly defined in the appended claim.

GENERAL DESCRIPTION Conventional tobacco smoke, more particularly conventional cigarette smoke, contains substantial traces of metals, and especially of transition metals, e.g., nickel, cobalt and iron, and such materials are reported to be toxic and carcinogenic to animals.

Thus, it has been reported in a paper by the Drs. F. W. Sunderman (Sr. and In), based on tests of six diflFerent brands of cigarettes, that nickel carbonyl containing from 0.4 to 0.6 microgram nickel per cigarette (corresponding Patented Nov. 29, 1966 "ice to about 20% of the total nickel of the tobacco) passes through the butt and filter of conventional plain or filter cigarettes, reaching the smoker (Medical Science, page 617, May 25, 1961; American Journal of Clinical Pathology, 35, 203 (1961)). In studies with rat-s, small amounts of nickel carbonyl were found by the Drs. Sunderman to be carcinogenic. The nickel delivered in the smoke drawn from the butt ends of the cigarettes amounted to up to 8 micrograms nickel per pack of 20, or 23.5 micrograms nickel as nickel carbonyl per pack of 20 of unfiltered cigarettes; and up to 12 micrograms nickel or 35 micrograms of nickel as nickel carbonyl per pack of filtered cigarettes. On the basis of their studies cumulative exposure to these quantities of nickel was suggested by the Drs. Sunderman to be a possible cause of the so-called smokers puhnonary cancer. Based on the reported figures, a person who smokes a pack of cigarettes per day over a period of a year subjects himself to about one and one-half times the amount of nickel required to induce pulmonary cancer in rats, which are considered to be notably resistant to pulmonary cancer.

Aside from the nickel reported, it has been found that traces of volatile cobalt and iron are also present, apparently as carbonyls, in cigarette smoke. The cobalt is present in somewhat smaller amounts than the nickel, about 1.3 micrograms of cobalt passing the filters per pack of filter cigarettes; and the iron is present in at least about twice the amount of nickel in the smoke of some brands of cigarettes.

Aside from the carcinogenic aspects of metal carbonyls reported by the Drs. Sunderman, it has long been known that such metals are highly toxic and dangerous materials even in trace amounts. Th-us Sax, Handbook of Dangerous Materials, published in 1951 by Reinhold Publishing Company, New York, prescribed a maximum allowable concentration of cobalt in the air as 0.4 part per million, and the Twenty-Second American Conference of Government Hygienists in April 1960 placed the maximal atmospheric concentration of nickel carbonyl for a working day at 1 part per "billion (AMA. Arch. Environmental Health 1, -144, year 1960). Iron carbonyl is also considered to be toxic, although less toxic than nickel and cobalt carbonyls. Accordingly, the cumulative toxicity effects of these three metals in tobacco smoke can be expected to be greater than that reported for nickel alone.

Likewise, aforesaid Drs. Sunderman in the above cited paper, demonstrated that cigars and pipe tobacco contain nickel in amounts similar to cigarette tobaccos, and similar amounts of nickel per gram of tobacco smoked can reach the smoker. Some pipe tobaccos contain 6 micrograms nickel per gram of tobacco, 6 micrograms cobalt per gram of tobacco and over 400 micrograms iron per gram of tobacco, of which over a microgram of each metal per gram of tobacco smoked can reach the smoker in conventional methods of smoking.

Hence it is evident that the quantities of transition metal present in the smoke from conventional plain and filter cigarettes and from cigars and pipe tobacco exceed the quantities deemed objectionable by the above authorities.

By the present invention such content of transition metal may be reduced in, or practically eliminated from, the tobacco smoke from such smoking articles, and this invention thus can serve as a safeguard to smokers against excessive exposure to such metals.

The new process for the treatment of tobacco smoke is based on the. reduction of transition metal content of tobacco smoke by the formation of non-volatile complexes or low-volatility complexes or salts by combination of the metal carbonyl or other metal content of 5 the tobacco smoke with a ligand, which for the purposes of this invention said ligand is an aromatic compound having a combination of at least one hydroxy radical and at least one other polar radical attached to the same aromatic nucleus, which compound acts as a complexing agent to form complexes of low volatility with transition metal content of tobacco smoke in the presence of other constituents of tobacco smoke, more particularly in the presence of moist carbon dioxide. The practice of the invention does not depend on the formation of exact empirical complexes since mixtures of such complexes may be formed with equal benefit for the process. Thus the ligands of this invention are principally aromatic compounds having one or more hydroxy (oxy) radicals attached to aromatic nuclei and such hydroxy groups in most of these ligands are in the ortho position to certain other groups which, with said hydroxy group of said compounds capable of forming relatively stable salts or complexes, or chelates of certain transition metal compounds, e.g., the carbonyls of nickel cobalt and iron.

Ligands hereof containing transition metal chelating groups and including thereamong at least one hydroxy group can be represented by the following Formula A:

i'1x in which the position of the double bond may be shifted, as it is part of an aromatic ring, and in which x is selected from those other radicals which in'combination with the ortho-hydroxy radical are capable of complexing certain transition metal compounds and such other radicals include:

TABLE A Marknsh Group of Radicals from which the Radical (x) in the Formula A is selected Ligand Group Comprising both radical (x) and the hydroxy radical ortho thereto 1. Carbonyl [(3:01 2. Carboxyl I: 0:0]

o-Hydroxy-carbonyl.

o-Hydroxy-arnide. o-Hydroxy-N-monosubstituted 5O amades. o-Hydroxy-N-disubstituted amides.

o-Hydroxy-azomethiue.

o-Hydroxy-azo. 5 5

When the ligands hereof have chromophore and/orauxochromophore groups they are colored, for example, the mordant type dyes have metal complexing groups 7 similar to those set forth in Table A above and therefore such mordant dyes in their unmordanted form may be employed as ligands for the purposes of this invention and the members of the mordant class of dyes are set forth throughout pages 1405-1616 of volume 1 (second edition 1956) of the Colour Index (edited by The Society of Dyers and Colourists, and The American Association of Textile Chemists and Colorists).

Iron, nickel and cobalt or other transition metal compounds present in tobacco smoke will combine with unmordanted mordant dyes in the presence of other ingredients of tobacco smoke.

Thus mordant dyes in their unmetalized form (unmordanted form) which are relatively non-toxic and capable of complexing or combining with the transition metals of tobacco smoke are considered ligands for the purposes of this invention.

This invention comprises:

(1) the method of treating tobacco smoke which comprises reducing the content of transition metal therein by contacting said smoke with a ligand as herein described;

(2) a filter element for reducing the transition metal content of tobacco smoke, said filter element including a substance comprising a ligand as herein described;

(3) a new article of manufacture, a cigarette having exposed in the path of the tobacco smoke therein means for reducing the content of transition metal thereof, said means comprising a ligand; and in this invention the term ligand means a substance which contains at least two functional groups which are attached to two adjacent carbons of an aromatic moiety and one of said functional groups comprising a hydroxy group and the other of said functional groups being a group having atoms selected from the class consisting of oxygen, nitrogen and combinations of these atoms and said other group being selected from the class consisting of carbonyl, carboxyl,

amide including N-mono-substituted and N-disubstituted amides, azomethine, azo, nitroso, oxazone, oxazine, lactone, oxy and combinations of such groups and said ligand being capable of removing transition metal compounds from tobacco smoke.

Thus volatile metal compounds in the cigarette smoke by the present invention are converted to non-volatile complexes by contacting the smoke with one or more ligand aromatic ortho-hydroxy compounds as above defined.

The complexes are formed by passing the smoke containing the metal compounds into contact with one or more of said ligands or over or through a filter material acting as a carrier body for the ligand material, and preferably comprising fibrous material, for example, cellulose ester tow, e.g., cellulose acetate tow prepared with the ligand thereon and/or therein, or wholly or partly coated with the ligand or with material such as activated carbon carrying the same.

To remove the transition metal compounds at least in part from tobacco smoke the ligands hereof are interposed in the path of said tobacco smoke as for example by depositing 0.01 to 10% preferably 0.5 to 5% by weight of such ligand material on the filter or other material located in the path of the tobacco smoke.

In the practice of the invention for example in making tobacco smoke filters one or more of the, ligands or complex-forming compounds or components with or without a solvent or plasticizer are preferably dispersed onsolid adsorbents; for example, the liquid or complex-forming components may be vaporized onto an adsorbent material, or a solution of a ligand may be applied to adsorbent material such as carbon, e.g., activated carbon, silica, pumice, vermiculite, clay, asbestos, polyesters, poly-' styrene, and cellulosic materials, e.g. cotton, cellulose, cellulose acetate, cellulose acetate-butyrate, cellulose propionate, tobacco, and other absorbing materials having a high surface area per unit weight or per unit volume. I

The ligand material of the present invention may be incorporated in or with the smoke-permeable bases, carriers or filters which themselves may embody various adhesives, adsorbents and surface area augmenting ma- .terials, and such incorporation of ligand material also may be made during the manufacture of the filter material or filters and thus such ligand materials can be incorporated with the materials and during the processes as disclosed, for example, in U.S. patents as follows:

The invention as above disclosed will be more fully understood by reference to the following examples of materials which may be employed as ligands for the practice of this invention and which examples are to be taken as illustrative and not restrictive of the invention.

1. The o-hydroxy-carbonyl ligand.The ligands of this group embnace the structure,

and include the following sub groups of ligands:

1(a). The aromatic hydroxyl-ketone Zigands.'lhis group of o-hydroxy-carbonyl ligands having the formula in which R R and R are radicals selected from the :group consisting of hydrogen, C to C hydrocarbon radicals (including alkyl, aryl, alk-aryl, aralkyl, cycloalkyl, alkylcycloalkyl radicals), =00, CHO, COOH, OH, OR, NO NHCOR, sO NH -SO NHR, -SO NRR, SO R, -SO H, CONI-I -CONHR, -CONRR, NI-I NHR, -NRR and halogen radicals; and R is a C to C hydrocarbon radical.

Usable as ligands of this group are compounds heretofore used as mordant dyes as for example those represented by Formulas I and II hereafter and the like as follows:

(I) HO OH HO ("J-CH Allzarine Yellow C (0.1, No. 57000) (H) HO OH Alizar'ine Yellow A (OJ, :No, 57005) The CI. numbers as used herein refer to compounds heretofore employed as dyes or dye intermediates and such C.I. numbers in the above cited Colour Index 2nd Edition (1957). Where, in the Colour Index, the Cl.

number cited refers to a metalated dye, e.g., with copper, chromium, cobalt, nickel or iron, it is to be understood that as a ligand hereof the compound should be in unmetalated form in reference to these metals.

1(b). The naphthaquinone ligands.The o-hydroxycarbonyl ligands of this group have one of the formulae OH OH n n 0 0H 0 wherein R and R are radicals selected from the group consisting of NHC H -O-C H5 OH, SO H and hydrogen radicals.

Usable as ligands of this group are compounds heretofore employed as naphthaquinone dyes and designated by the 01. numbers: 57010, 57015, 57020, 57025 and 57030.

1(a). The anthraquinone ligands.-This group of ohydroxy-carbonyl ligands have the formula N 0 OH O R H H v R1 R Il -E l R R2 R2 v R3 R3 H O 0 *Including the isomer with ;N in starred position,

wherein R and R are selected from the radicals consisting of OH, SO H, -NO COOH, NH; and hydrogen.

- Usable as ligands of this group are compounds here t-ofore employed as anthraquinone dyes and designatedby the Cl. numbers:

and the like.

1 (d). The qnthmhydroxy phthalein ligands.'I':his group of o-hydroxy-carbonyl ligands is represented by compounds heretofore employed as anthrahydroxyphth-alein dyes and designated by the Cl. numbers 45505 and 45510, and the like.

2. The hydroxycarboxyl ligands.-The ligands of this group embrace the structure and include the following subgroups of ligands.

2(a). The substituted phenyl-o-hydroxycarbonyl ligands.Represented by the formula wherein R R and R are similar radicals to those set forth under 1(a) heretofore;

7 2(b). The substituted naphthyl-o-hydroxycarbonyl ligands.Represented by the formula wherein R R and R are similar radicals to those set forth under 1(a) heretofore.

Examples of these o-hydroxycarboxyl ligands include:

2(a). The azo-O-hydroxycarboxyl ligands.The ligands of this group include the monoazo, disazo and trisazo compounds with the lower molecular weight compounds usually being preferred for such can bind a greater quantity of metal based on the weight of the compound. These compounds, if desired, may be ap plied to the filter material as a sodium salt, as for example: 1

COONa =C.I, Mordant Yellow 18 (0.1. "N0. 13990) and may then be acidified at least in-part to yield the:

free o-hyd-noxycarboxylic acid v coon 2(c-1). The monoozo o-hyiiroxycarboxy ligands include ligands represented by the formulae:

wherein R R and R are similar radicals to those set forth under 1(a) heretofore.

- Usable as ligands of this group are compounds here= to-fore used as dyes and designated by the Cl. Nos:

2(c-2). The disazo-o-hydroxy-carboxyl ligands.'Ilhe ligands of this group are similar in structure to the monoazo compounds set forth under 2(c1) heretofore except such are disazo compounds having two azo groups and because of their higher molecular weight are less preferred.

2(c-3). The trisazo and polyazo-o-hya'roxy-carboxyl ligands.Tlhe ligands in this group are similar in structrue to the inonoazo compounds set forth under 2(0-1) heretofore except that these compounds have three azo groups and therefore because of their higher molecular weight are less preferred.

2(d). The triarylmethane-o-hydroxy-carboxyl ligands.Liga.nds of this group include [the triphenyl-metlhane o-hydroxy-carboxyl ligands such as the compounds heretofore used as dyes designated by the Cl. numbers:

in which R and R are radicals selected from the C to C hydrocarbon radicals.

4. The o-hydroxy-azomethine ligands.T-his group of o-hydroxy-azomethine ligands have the common radical represented by the formula in which R is a hydrocarbon or substituted hydrocarbon radical and include ligands represented by the following formula including the hydroxy-oximes, hydroxy-aldimines, hydroXy-ketimines and such compounds as the following wherein R and R are similar radicals to those set forth under 1(a) heretofore.

5. The o-hydroxy-azo ligands.'1"he o-hydroxy-azo ligand can embrace the structure \CN=N- and include the following subgroups of ligands:

(a1). Monoazo and disazo ligand compounds.- Having the o-hydroxy-azo group including such structures as represented by the following:

and similar disazo compounds in which R and R are radicals selected from the radicals set forth under 1(a), erg. CH --NO Cl, SO H, COOH, --NH CONH or hydrogen radical etc.

5 (b). The 0,0-dihydr0xy-azo ligands.--These ligands embrace the structure and include compounds heretofore employed as :monoa'zo, disazo and polyazo dyes. They have the structural forwherein R R and R are similar radicals to those set forth under 1(a) heretofore.

Examples of the ligands of this group are the o,o-dihydroXy-azo ligand compounds, which compounds have heretofore been employed as dyes designated by the Cl. numbers:

Among the above examples of ligands are also included dihydroXy-azo ligands which have a nitrogen containing ring, e.g., a pyrazole ring or a quinoline ring such as the following:

6. The o-hydroxy-nitroso ligands.Li:gands having the o-hydroxy-ni troso group embraced !by the following structures include compounds such as:

l-nitroso-2-naphthol-6-sulfonic acid 1nitroso-2-naphthol-4-sulfonic acid l-nitroso-Z-naphthol 2-nitroso-1-naphthol Chrornotropic acid dioxime Nitnosochromotropic acid 2,4-dinit1'os0-3,5-dihydroxy-tolnene 2,4-dinitroso1,3-dihydroxybenzene o-Nitrosocresol 2-nitlroso-1-naphthol-4-su1fionic acid 4-nitrosoresorcino1 Nitroso-R-salt p-Nitroso-thymol 7. The o-hydroxy-oxazo ne ligands.Ligands having the ortho-hydnoxy-oxazone lgroup are exemplified Iby compounds heretofore'used as dyes and designated by the Cl. numbers 51405, 51410.

8. The o-hy-droxy-oxazine ligands.-Ligands having the ortho-hydroxyoxazine group 1 1 include compounds heretofore used in dyes and identified by the ()1. numbers 51025, 51030, 51040, 51045, 51050, 51060, 51065 and 51070.

9. The hydroxy-lactone ligands.--Ligands of this class have both the hydroxy group and a laotone group and as such ligands may be employed compounds heretofore used as dyes and identified by the Cl. numbers 55000, 55005 and 55010.

Among the compounds included in subclasses 1 through 9 above are the mordant dyes and for the purposes of the present invention the mordant dyes are incorporated in the cigarette filters in essentially unmordanted form, and thus are present in a form capable of combining with and extracting from tobacco smoke the transition metal con-tent thereof.

By the term unmordanted is meant the mordant dyestuif is essentially free of metal ions which mordant or insolubilize the dyestutf, e.g., is essentially free of aluminum, iron, manganese, chromium, nickel, cobalt, copper, zinc, calcium, lead and other metals including the transition metals of sub-groups 1V, V and VI of the Periodic Table. For purposes hereof the mordant dyestuif is sometimes employed in the form of a water soluble salt, e.=g., an alkali metal, ammonia or amine salt.

10. The o-dihya'mxy ligands.The ligands of this gnoup have at least one aromatic radical with two hydroxy groups in ortho position to one another and such ligands embrace the following'structure:

Included among the compounds of this class is pyrogallol, catechol and the alkyl substituted catechols, pyrocatechol, methyl pyrocatechol, the 1,2,3-trihydroxybenzene, the 1,2,4-trihydroxy benzene, the tetrahydroxyabenzenes, hexahydroxybenzene, similar compounds of the naphthalene series gallic acid, m-digallic acid, the tannic acids, the tannins protocatechuic acid, 1,2-dihydroxybenzene-3,5- disulfonic acid, 9-methyl-2,3,7-trihydroxy-6-flurone, and the dyestuffs having such structure as for example HO OH SO H pyroca-techol violet EXAMPLES In the following examples wherein coating procedures are not otherwise described, filters were prepared as follows: The manufacturers filters were removed from Brand A filter cigarettes and 0.5 ml. of an aqueous and/or alcoholic solution of the ligand was added dropwise to the filters. The individual filters average 0.125 g. in weight. The proportions of water and alcohol in the solution were adjusted for ligand solubility considerations. Where the ligand was a dyestuff and the acid form of the dye was desired the major portion of the solvent mixture used was alcohol, and the required amount of hydrochloric acid was added thereto to convert the commercialsodium or ammonium salt of the dye to its acid form. The inorganic salts present in most commercial dyes were removed by dissolving the dye in a solvent e.g., alcohol and filtering or the insoluble salts were allowed to settle out and only the soluble onganic dye material was added to the cigarette filters. When the salt of the dye was desired as the coating agent the alcohol was diluted with water, thus increasing the dye salt solubility. The amount of dye present in the 0.5 ml. of solution was varied to give from 1% to 10% as desired. The filters were observed to be substantially uniformly colored by the 0.5 ml. of dye solution, and were dried at 50 C., atmospheric moisture equilibrated at room temperature and about 70% humidity, and each filter was employed for filtering the smoke of one Brand A cigarette from which the manufacturers filters had been removed. A sample for analysis consisted of smoked filters.

An alternate procedure was to use the dyed filter as a back-up filter for smoking Brand A filter cigarettes. In this procedure a direct comparison of effectiveness of the transition metal absorptions by conventional filters and the filters of this invention is possible.

The analysis of the tobaccos of the Brands A, B, C and D employed in these tests showed the following range of metal contents.

Since such variations occur in the metal content of the same brand of cigarettes it is apparent that the smoke will vary widely in metal content and each lot of cigarettes must have control tests run with conventional filters for comparison with the ligand treated filters of this invention.

Example 1 A suspension-solution was prepared by stirring 1 gram of the red compound 2,4-dibenzene-azoresorcinol, with a mixture of 60 g. benzene and 15 g. isopropanol. Cellulose acetate tow (5.024 g.) was immersed in the resultant suspension-solution for 18 hours and then, with 50 g. of

' absorbed liquid, was placed in a C. air stream for 2 Manufacturer's Back-Up Filter Transition Metals Filter (micrograms/ I (micrograms/ cigarette) cigarette) Iron 15.0 36.7 Cobalt None 0. 02

Example 2 Five grams of Cl. Mordant Red 7 (CI. 18760) was dissolved in 400 grams warm Water and 7.928 g. of cellulose acetate tow was immersed in the solution for five minutes. The cellulose acetate material after drying at 70 .C. was equilibrated with the atmospheric moisture and the tow contained 7.7% of the dry material. Sixty Brand A filter cigarettes were smoked in pairs using a 0.264 g. ($0.005 g.) portion of the dyed tow as backup filter material for each pair of cigarettes. Analysis of terial is as follows:

tf f' I CH3 Example 3 Five grams of Cl. Mordant Yellow 30 (CI. 18710) was dissolved in 400 grams warm water as in Example 1 and 7.734 g. of cellulose acetate tow was immersed in the solution for 5 minutes, squeezed, immersed in acid, squeezed dry, and dried at 70 C. The equilibrated sample contained 2.5% of the dye ligand material. Sixty Brand A filter cigarettes were smoked in pairs as in Example 2 using a 0258:0005 g. portion of the dyed tow as a back-up filter. Analysis of the used back-up filters showed absorption of 17.6 micrograms of iron, 0.30 microgram of nickel and 0.43 microgram of cobalt per cigarette smoked vs. 3.2, 0.17 and 0.18 micrograms of iron, nickel and cobalt absorbed respectively by the manufacturers filter per cigarette smoked. The structure of the dye ligand material of this example is:

H; Example 4 Example 2 was repeated using the dye C.I. Mordant Blue 1 (CI. 43830) with 8.3 grams of tow. The wet material was immersed in dilute hydrochloric acid solution and dried. The coated tow was used as back-up in smoking sixty Brand A filter cigarettes which were smoked in pairs using a 0.277 g. (:0005 g.) portion of the dyed tow as back-up filter for each pair of cigarettes. Analysis of thirty used back-up filters showed absorption of 0.76 microgram of nickel per cigarette smoked vs. 0.17 microgram nickel absorbed per cigarette for the manufacturers filters.

The structure of this dye ligand material is:

COOH

Example 5 Example 4 was repeated but omitting the acid treatment, thus allowing the Cl. Mordant Blue 1 ligand dye to remain as the sodium salt of the structure shown in Example 4 (the treated tow absorbed 4% dry). Smoking of 60 Brand A filter cigarettes in pairs was conducted using a 0.262 g. (10.005 g.) portion of the tow as backup filter for each pair of cigarettes. Analysis of the used back-up filters showed absorption of 20.0 micrograms iron, 1.8 micrograms nickel and 0.43 rnicrogram of cobalt per cigarette smoked in comparison with 3.2, 0.17 and 0.18 micrograms of iron, cobalt and nickel per cigarette respectively absorbed by the manufacturers filter during smoking.

' 14 Example 6 The dye C.I. Mordant Red 3 (Cl. 58005) was used as the sodium salt in this experiment to coat 7.55 g. of cellulose acetate tow to give 1.3% dry dye content. The smoking test was conducted as in Example 2. The back-up filters, of this invention showed absorption of 77.5 micrograms iron, 0.61 micrograrn nickel and 0.235 microgram cobalt per cigarette smoked vs. 3.2, 0.17, and 0.18 microgram iron, nickel and cobalt respectively per cigarette for the smoked manufacturers filter. The structure of this dye is as follows:

Example 7 Example 2 was repeated using 7.55 g. cellulose acetate tow containing about 2.5 total acidified Tartrazine dye C.I. Food Yellow 4 (Cl. 19140) contents. Smoking was conducted with sixty Brand A filter cigarettes as in EX- ample 2, but using the presently prepared ligand-coated cellulose acetate as back-up filter. Analysis of the filter material after use showed absorption of 64.5 micrograms of iron per cigarette smoked in comparison with 0.75 microgram absorbed by the manufacturers filter per cigarette smoked. The structure of this ligand dye is as follows Example 8 FD & C Yellow No. 6 (CI. 15985) was-used to coat cellulose acetate filters of Brand A filter cigarette. The aqueous solution of the commercial dye (5 g. in 400 ml. water) coated the tow with the sodium salt and the wet tow was immersed in 1% hydrochloric acid solution to convert it to the free acid form:

Non-dyed Manu- Dyed Manu- Transitron Metal facturers Filters facturers Filters (micrograms/cigarette) (micrograms/cigarette) Iron 1. 0 3. 7 Nickel 0. 16 0. 27

Example 9 Chrome Fast Black FWX or Cl. Mordant Black 5 (CI. No. 26695) was employed as in Example 8 to dye filters taken from Brand A filter cigarettes. About 8% of total dye material was found absorbed by the dried dyed tow. The smoking test conducted as in Example 8 showed the following metal absorptions in comparison with the controls:

Example 10 Example 8 was repeated but using Chrome Fast Brown EBC or Mordant Brown 1 (Cl. No. 20110) as the dye to treat the cellulose acetate tow and the dye salt was not acidified. The dyed filter contained about 3.5% total dye components. Comparative data of metal absorption from the smoke using the non-dyed and dyed filters were as follows:

Non-dyed Manu- Dyed Manu- Transition Metal faeturers Filters facturers Filters (micrograms/cigarette) (micrograms/cigarette) Iron None 71. 8 Nickel 0. 01 0. Cobalt None 0. 09

The structure of the dye used in this example is as follows:

N=N I N=N OzN HzN NH: SO Na Example 11 This example is similar to Example 8 except that Superchrome Brilliant Violet NR or Cl. Mordant Violet 1 (Cl. No. 43565) was employed, without acidification. The filters contained 8.5% dye material. In an identical smoking test as used in Example 8 the following absorptions of metals were obtained:

This example was made similar to Example 7 but Tartrazine (FD & C Yellow No. 5) was used' without 16 acidification as the dye material. About 2% dye'materials were absorbed by the filter in dyeing. Analyses of filters after smoking showed the following data:

Non-dyed Manu- Dyed Manu- Transition Metal facturers Filter facturers Filter (micrograms/cigarette) (micrograms/cigarette) Iron 1. 0 3. 0 NickeL 0. 16 0. 35

Cobalt. 0. 0 0. 016

The structure of the dye of this example was:

.( JOONa Acidification of the dye ligand improves the ability of the filter for absorption of metals from the smoke.

Example 13 Uncoated Tow Ligand Coated Tow Transition Metal 7 (micrograms/cigarette) (micrograms/cigarette) Iron.-. 14. 3 106. 4 Nickel. 0. 12 0. 18 Cobalt 0. 045 0.30

Example 14 In this example the ligand material was gallic acid. Gallic acid coated celluloseacetate tow was prepared containing about 4.3% gallic acid. The coating solution consisted of 5 g. gallic acid, 200 g. isopropanol and 50 g. water, the amount of tow used was 17.295 'g., drying time was 15 hours 70 C. and atmospheric moisture equilibration time was 29 hours. Smoking tests were conducted with 30 portions of the coated tow each portion weighing 0.260 g. :L 0.005 g.; each portion was used as a filter for smoking two Brand D non-filter cigarettes. Similar smoking tests with uncoated tow were also carried out. Analyses of the filters with and acid solution in water to prepare a filter material con-v taining 19.2% tannic acid. The volume of solution was ml., the weight of cotton was 20.450 g., the immersion time was five minutes, the Wet weight was 75 grams, the drying time was 15 hours 70 C., and the atmospheric moisture equilibration time was 8.5 hours. Thirty portions of this ligand coated cotton'were weighed out 0.308 1 0.005 g. and each portion was employed as a back-up filter for smoking two Brand A filter cigarettes. The GQIBbiuGd back-up filters and the manufacturers fil- 17 ters from smoking sixty cigarettes were analyzed for iron, nickel and cobalt. The following micrograms of metals were found to have been absorbed per cigarette smoked.

Sixty filters were removed from Brand A filter cigarettes, and were coated by adding to each filter 0.5 ml. of a filtered solution of 5 g. of FD & C Red No. 4 dye in a mixture of 100 ml. water, 100 ml. isopropanol and 1.5 ml. 37% hydrochloric acid. After drying and equilibrating the filters were found to contain about 12% dye. The structure may be represented by the following formula:

S 11 OH Sixty Brand A cigarettes without the manufacturers filters were smoked using as filter one of the above coated filters. After use in smoking, the filters were combined and analyzed for iron. The results showed that 17.25 micrograms of iron had been absorbed per cigarette smoked. In an identical smoking test using the manufacturers filters only 86 micrograms of iron were absorbed per cigarette smoked.

Example 17 A solution of ligand material was prepared by dissolving 5 g. Alizarin Red S ((11. 58005) in a mixture of 200 ml. isopropanol and 50 ml. water containing 0.56 g. of hydrogen chloride, and filtering to remove inorganic salts. Sixty filters were removed from Brand B cigarettes and were impregnated with the filtered Alizarin solution by adding 0.5 ml. of said solution to each of the sixty filters. The dried and equilibrated filters were found to contain about 6% of the ligand material represented by the following formula:

II o This is the acid form of the ligand material of Example 6.

Sixty of the Brand B cigarettes, from which manufacturers filters had been removed, were smoked using one of the coated filters above prepared for each cigarette. The combined filters after smoking were analyzed for nickel and were found to have absorbed 0.64 micrograms of nickel per cigarette smoked. Simultaneously a control smoking test was made with 60 Brand B cigarettes with the manufacturers filters. The combined manufacturers filters after use showed absorption of 0.0 microgram of nickel from the smoke, thus demonstrating the eifectiveness of the ligand material.

Example 18 Sixty filters removed from Brand A cigarettes were coated as in Example 16 using for each filter 0.5 ml. of a filtered solution prepared by dispersion of 5 g. Indigotine (FC & D Blue No. 2, CI. 73015) in a mixture of ml. water, 150 m1. isopropanol and 2 ml. concentrated HCl. The dried equilibrated filters contained about 3.6% of the dye represented by the following structure:

Ho s S0311 c o is 1'1 Sixty Brand A cigarettes were smoked as in Example 16 using one of these above coated filters in place of the manufacturers filters. The filters were found by analysis to have absorbed 28.9 micrograms of iron per cigarette smoked. This is to be compared with 8.6 micrograms of iron absorbed per cigarette by the manufacturers filter.

Example 19 Sixty filters were removed from Brand A cigarettes and were coated by adding to each filter 0.5 ml. of a filtered solution made up by dispersing 5 g. of National Superchrome Garnet Y (CI. 14290) in a mixture of ml. isopropanol, 100 ml. water and 0.55 g. hydrogen chloride. The dried equilibrated filters contained about 9.7% of the dye of the following structure:

OH HO In a smoking test as in Example 16 with sixty Brand A cigarettes (with manufacturers filters removed) the filters absorbed 0.4 microgram nickel per cigarette smoked vs. none for the control.

Example 20 Five grams of polygalacturonic acid was dissolved in 400 g. water at 80 C- and 7.507 g. of cellulose acetate tow was immersed therein for ten minutes. The dried coated tow after equilibration with thewmoisture in the laboratory air showed a 13.5% content of the polygalacturonic acid. The coated tow was divided into thirty portions, each weighing 0289:0005 g. and each portion was used to filter the smoke of two Brand D non-filter cigarettes. The combined filters after smoking showed absorption of 9.2 micrograms of iron per cigarette smoked. In a control test 300 Brand D cigarettes were smoked using cellulose acetate tow filters made by the manufacturer of Brand D cigarettes and these commercial filters, in the absence of the ligand, removed only 2 micrograms of iron per cigarette.

The effectiveness of the ligands hereof in removing trace metals from tobacco smoke can be improved in most instances when such ligands are combined with a suitable plasticizer. By the term suitable plasticizer is meant a cohol, ether, ester groups or combinations of such groups and examples of such include the following: Triacetin (glyceryl triacetate), glycen'ne, glyceryl mono-oleate, glyceryl mono-ricinoleate, 2-butoxyethano1, butoxyethyl laurate, diethylene glycol, diethylene glycol mono-ricinoleate, olive oil, butyl oleate and for additional plasticizers see Table 15.3 (pages 904-927) of The Technology of Solvents and Plasticizers by Arthur K. Doolittle, published 1954 by John Wiley & Sons, Inc., New York, New York.

While there have been described herein what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that modifications and changes may be made without departing from the essence of the invention. It is therefore to be understood that the exemplary embodiments are i1- lustrative and not restrictive to the invention, the scope of which is defined in the appended claim, and that all modifications that come within the meaning and range of equivalency of the claim are intended to be included therein.

We claim:

A process for the purification of tobacco smoke from a smoking article by the removal of volatile metal compounds therefrom, which comprises passing said smoke through a filter into the mouth of the user down stream therefrom, said filter comprising a ligandoompound having the formula:

II R2 0 in which R R and R are radicals selected from the group consisting of hydrogen, C to C hydrocarbon radicals, :CO, --CHO, COOH, OH, OR, NO NH--CO-R, -SO NH SO NHR, -SO NRR, SO R, SO H, CONH CONHR, CONRR, NH NHR, NRR, and halogen radicals; and R is a C to C hydrocarbon radical; said ligand compound being other than a mordant dye.

References Cited by the Examiner UNITED STATES PATENTS 2,815,760 12/1957 Schreus et al 131208 2,886,591 5/1959 Lautenschlager et a1. L 131--10 X OTHER REFERENCES Organic sequestering Agents, by Chabbrek and Martell, published by John Wiley & Son (1949).

The Merck Index, published by the Merck Co. (1960),

' p. cited.

SAMUEL KOR-EN, Primary Examiner.

M. D. REIN, Examiner. 

